A GROUP OF SPORANGIA (SPORE-CASES) 
Each of these capsules (here magnified about 100 times) contains a large number of ovoid spores, 
the reproductive cells, three of which can be seen in the upper left-hand corner. 
Although 
this method of reproduction is called sexual, the spores themselves have no sex—or rather, 
they are a combination of the two sexes in one. 
When they become ripe they are shed 
upon the ground, where they germinate and give rise to little sexual plants, called prothallt, 
shown in the next illustration. 
After the spores have been sown on 
the surface of this medium, the pot is 
covered with a piece of glass and 
then set in a saucer filled with water, 
in a partly shaded propagating frame. 
The saucers are placed on clean cinders 
over which lime has beenscattered. This 
keeps away insects, worms and molds. 
At the end of four weeks or more the 
spores begin to germinate and form the 
so-called prothalli—heart-shaped, leaf- 
like plants which attain a diameter of 
a quarter of an inch, when fertile. 
From each of these develops a new fern. 
When the first leaves appear the 
prothalli should be removed in small 
clumps or singly with.a pair of forceps 
and planted half an inch apart in 
flats or pans containing leaf mold to 
228 
(Fig. 20.) 
which a little finely sifted soil has been 
added. Later they are transferred into 
214-inch pots. 
The seedlings obtained in this manner 
are, as they grow, carefully watched for 
the appearance of new types, which 
are isolated and studied. 
Most of our commercial varieties 
are sports of N. exaltata bostoniensts. 
This variety probably originated 
near Boston some thirty years ago. 
The first recorded sport of commercial 
importance occurred during the early 
part of 1898 and since then there have 
been produced over sixty-five commer- 
cial varieties of which about fifty are of 
American origin. 
In order to produce new types it is 
necessary to raise a large number of 
